1. Field of the Invention
This application is related to U.S. patent application Ser. No. 07/358,688 filed May 30, 1989. and assigned to the same assignee as the present invention.
This invention relates generally to batteries and more specifically to batteries which benefit from electrolyte circulation.
It has been known that in secondary batteries, such as those typified by lead acid batteries using aqueous sulfuric acid or liquid electrolyte, that the electrolyte tends to stratify when cycled. The stratification becomes aggravated during charge and recharge, affects cell performance and reduces battery life time. Additionally, ambient heat and efficient distribution of the internally generated heat are problems where the electrolyte is essentially stagnant
2. Description of the Prior Art
The prior art is replete with examples of various devices used to circulate electrolyte in secondary batteries or otherwise prevent stratification. U.S. Pat. No. 916,320 issued on Mar. 23, 1909 to H. F. Joel illustrates a technique of tapering a center electrode in a circular battery and slanting the outer conical electrode relative to the separators such that the gas collecting on either side of the separator moves upward and accumulates in ever narrowing passageways, forcing electrolyte as bubbles up through orifices at the top and then over to the outside of the outer electrode where it moves downward. According to the patentee this draws the denser electrolyte from the bottom of the battery. U.S. Pat. No. 2,584,117 issued on Feb. 5, 1952 to Elrod Jr. also recognized the problem and proposed the use of an air blown device to aerate the electrolyte to alter the density thereof to create circulation. Still another, U.S. Pat. No. 4,283,467 issued Aug. 11, 1981 to Gutlich, et.al., discloses a device that also utilizes gas to alter electrolyte density. U.S Pat. No. 4,308,322 issued Dec. 29, 1981 to Hammar describes a pump within the battery comprising a gas collecting hood and passageways which utilize the generated gas to carry electrolyte as bubbles to the passageways, thus inducing circulation. Another design to reduce stratification is disclosed in U.S. Pat. No. 4,619,875 issued Oct. 28, 1986 to D. W. Stahura, et.al. in which the separator has a plurality of laterally extending concave ribs on the surface thereof that act to trap the more dense electrolyte.
U.S. Pat. No. 529,199 issued Nov. 13, 1894 to Schoop represents an early attempt to provide circulation of electrolyte by harnessing the energy created through changes in velocity of the vehicle utilizing the battery. Schoop describes several embodiments of pumps for accomplishing such circulation, one of which involves creating a hydrostatic head from laterally moving waves in the free electrolyte. As typified by Schoop, such pumps involving hydrostatic heads are generally defined by one wall spaced from the cell wall. The second wall extends a short distance above the surface of the liquid end, together with the cell wall, forms a mouth of the pump. An "outlet" of the pump is formed by the bottom end of the second wall terminating slightly above the bottom of the cell. The theory of operation of such a pump is that the mouth captures a portion of the liquid contained in the wave caused by changes in the velocity of the vehicle carrying the cell. Once captured, the additional liquid within the pump becomes a hydrostatic head and dissipates downward and out the opening between the distal end of the second wall as a current of electrolyte.
A significant drawback of hydrostatic pumps represented by Schoop, particularly the embodiment of FIG. 3 thereof, is the inability to cope with the "splashing" that occurs at the wall of the cell. For example, when the cell holding the liquid abruptly stops, the need of the liquid to exchange its momentum results in several disturbances. First, a laterally moving surface wave is generated which crests substantially at the wall in the direction of wave movement. Simultaneously, the underlying liquid impinging against the wall tends to move rapidly up the wall and literally causes a splash to occur at the crest of the overlying wave. The splashing, in effect, prevents the formation of any meaningful hydrostatic head within the pump. Pumps typified by Schoop resort to moving valve mechanisms which close against the pressure of upward liquid movement and open once the pressure subsides to allow the hydrostatic head to dissipate.
Application Ser. No. 07/201,042 filed May 31, 1988 and entitled "Internal Hydrostatic Pump For A Mobile Vehicle Battery", assigned to the same assignee of the present invention, discloses a simple and essentially maintenance free static pump for utilizing the laterally moving surface waves induced in the electrolyte. The vertical surge of the electrolyte, or splashing, is maintained at low levels due to geometrical differentials between upper and lower dimensions of the pump.
As the foregoing shall describe, applicants have further refined the aforementioned static pump to reduce the volume of the vertical surge of electrolyte occurring when a change of velocity is experienced and to isolate sediments occurring beneath the electrode plates.